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At least 19 recordsLinked to original sources
PubMed1992

Degradation of methyl and ethyl mercury into inorganic mercury by hydroxyl radical produced from rat liver microsomes.

Liver microsomes were prepared from Wistar rat by the Ca2+ aggregation method. Under various conditions, ethyl mercury chloride (EtHgCl) or methyl mercury chloride (MeHgCl) was incubated with the microsomal preparations. After the incubation, the amounts of inorganic Hg and hydroxyl radical (.OH) in the preparations were determined. Although the preparations alone produced a small amount of inorganic Hg and .OH, the addition of NADPH to the preparations increased both inorganic Hg and .OH production, which were further accelerated by the addition of KCN. The addition of Fe(III)EDTA, a .OH formation promoter, to the microsome-NADPH-KCN system increased inorganic Hg production, whereas the addition of diethylenetriamine pentaacetic acid, a .OH formation inhibitor, decreased inorganic Hg production. When .OH scavengers such as mannitol and dimethyl sulfoxide were added to this system, the inorganic Hg production decreased. These results suggested that the .OH produced from liver microsomes was responsible for the degradation of MeHg and EtHg. Since both .OH and inorganic Hg production decreased with a concomitant decrease in NADPH-cytochrome P-450 reductase activities, it is suggested that this enzyme may be involved in the microsomal degradation of MeHg and EtHg.

Animals↗
PubMed1979

Synthesis and identification of products derived from the metabolism of the carcinostatic 1-(2-chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea by rat liver microsomes.

Liver microsomal metabolism of 1-(2-chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea in the presence of reduced nicotinamide adenine dinucleotide phosphate and O2 was shown to produce seven metabolites that included the parent urea. A cytochrome P-450-dependent monohydroxylation of the cyclohexyl ring occurred in 3 positions, cis-3, trans-3, and cis-4, and on the methyl group to form a trans-4-hydroxymethyl derivative. In addition, monohydroxylation of the 2-chloroethyl carbon attached to the N-1 urea nitrogen yielded an alpha-hydroxy metabolite. A ring-hydroxylated derivative remained unidentified while the structures of all other such derivatives were established by comparison with compound synthesized, purified by high-pressure liquid chromatography, and characterized by mass spectral and nuclear magnetic resonance analyses. It was tentatively concluded that some parent urea is formed by a cytochrome P-450 dependent reaction because of a requirement for reduced nicotinamide adenine dinucleotide phosphate and inhibition by CO. Microsomes from rats pretreated with phenobarbital showed about a 3-fold increase in hydroxylation rate while phenobarbital-treated mice microsomes were induced 8-fold. However, in both species, the induced hydroxylation rate was about 4 nmol/min/mg protein. When microsomes from phenobarbital-induced rats were used, a mixture of 80% CO:20% O2 decreased the rate of formation of all metabolites to 14% of that in 80% N2:20% O2.

Animals↗
PubMedDate not supplied

Influence of pregnancy and folic acid on phenytoin metabolism by rat liver microsomes.

Liver microsomal suspensions from pregnant and nonpregnant Sprague-Dawley rats were assayed for NADPH-dependent metabolism of phenytoin to the hydroxylated products, 5-(rho-hydroxyphenyl)-5-phenylhydantoin (rhoHPPH) and 5-(3,4-dihydroxy-1,5-cyclohexadien-1-yl)5-phenylhydantoin (H2DIOL). UDP-glucuronic acid-dependent glucuronyltransferase activity for conjugating rhoHPPH was also measured. The specific activity for formation of rhoHPPH decreased by 35% in 21-day pregnant rats compared with nonpregnant rats, whereas specific activity for production of H2DIOL was increased approximately 2-fold on the 7th and 14th but not the 21st day of pregnancy. Because of a 25% increase in liver weight during pregnancy, the total hepatic phenytoin hydroxylase activity in pregnant rats (day 21) was not significantly different from that of nonpregnant controls. Folic acid treatment during pregnancy prevented the decrease in phenytoin hydroxylase specific activity. The KM for production of either rhoHPPH or H2DIOL was similar (90 micrometer) in pregnant (day 21) and nonpregnant animals. Thus, overall hepatic microsomal enzyme activity for metabolizing phenytoin was not significantly reduced during pregnancy in rats, although the ratio of H2DIOL to rhoHPPH was increased during the first two weeks. Folic acid may play a role in pregnancy-associated changes in phenytoin hydroxylase activity.

Animals↗
PubMedDate not supplied

Effects of pesticides on metabolism of steroid hormone by rodent liver microsomes.

Liver microsomal steroid hydroxylating enzymes and prostatic testosterone-5alpha-reductase were studied in rat and mouse. Organochlorine and organophosphate pesticides tended to inhibit liver steroid hydroxylations, while carbofuran slightly stimulated them. Neither species was consistently more sensitive to pesticide effects than the other. All the pesticides bound to cytochrome P-450, producing Type I spectral changes. Values of Ks ranged from 1.9 to 8.7 mM for organochlorine and organophosphate compounds. Affinity for carbofuran was much lower (Ks=100-200mM).

Animals↗
PubMed1975

Effect of rifampicin treatment on the metabolism of oestradiol and 17alpha-ethinyloestradiol by human liver microsomes.

Liver biopsies were obtained from four patients treated with rifampicin 600 mg for 6-10 days. Hepatic microsomes were incubated with an NADPH-regenerating system and the substrates [2,4,6,7-3H] oestradiol, [6,7-3H] oestradiol, [2,4,6,7-3H] ethinyloestradiol and [6,7-3H] ethinyloestradiol. The hydroxylation rates of these steroids at the labelled positions of rings A and B were determined by measuring the transformation of tritium into HTO by the microsomal enzymes. Comparison with previously published data showed that treatment with rifampicin caused a fourfold increase in the rate of hydroxylation of oestradiol and ethinyloestradiol at positions C-2/C-4 of ring A and C-6/C-7 of ring B. The acceleration of oestrogen hydroxylation by rifampicin was paralleled by an increase in microsomal cytochrome P-450, and also by microsomal reduction of rifampicin-quinone, a reactive metabolite of rifampicin. The increased aromatic hydroxylation of oestradiol and ethinyloestradiol leads to enhancement of their irreversible binding to microsomal protein. The data provide an explanation for the diminished efficacy of oestrogens in contraceptive formulations given to patients under treatment with rifampicin.

Adult↗
PubMed1977

On the aromatic hydroxylation of amphetamine in rat liver microsomes and perfused liver preparations: effects of long-term administration.

The liver microsomal p-hydroxylation of amphetamine to parahydroxyamphetamine (pOHA) was dependent on NADP and inhibited by carbon monoxide indicating the involvement of cytochrome P-450, SKF 525-A, fenfluramine and desmethylimipramine were the most effective inhibitors of this pathway of amphetamine metabolism. Repeated administraion of phenobarbital resulted in reduced p-hydroxylation of amphetamine in vitro. Chronic administration of amphetamine reduced the microsomal p-hydroxylation of amphetamine without apparent changes in the cytochrome P-450 levels or in the activity of NADPH-cytochrome c reductase. The aromatic hydroxylation of aniline and the demethylation of ethylmorphine was not affected by this treatment. However, the 455 nm complex formed during the microsomal metabolism of N-hydroxy-amphetamine was increased by the long-term administration of amphetamine. These results indicate some pecularities of the in vitro hydroxylation of amphetamine by rat liver microsomes. Amphetamine disappeared from the perfusate of the perfused liver at the same rate in rats given a single dose of amphetamine and in rats given amphetamine orally for four weeks. The excretion of pOHA and its conjugate increased at 60 and 90 min. and 30, 60 and 90 min. respectively in the perfusate of the same experiment as compared to the controls. The total excretion of radioactive amphetamine metabolites at the end of the perfusion was increased in the perfusate and reduced in the bile compared to the control experiment.

Administration, Oral↗
PubMedDate not supplied

Correlation of 14C-griseofulvin metabolism in rat liver microsomes, isolated perfused rat livers, and in rats with bile duct cannulas.

The metabolism of 14C-griseofulvin has been compared in rat liver microsomes, isolated perfused rat livers, and rats with bile duct cannulas. In all three preparations, 4-desmethylgriseofulvin and 6-desmethylgriseofulvin were the major metabolites. The ratio of total 4-desmethylgriseofulvin to 6-desmethylgriseofulvin formed was 1.20, 0.89, and 1.01 in liver microsomes, isolated perfused livers, and rats with bile duct cannulas, respectively. After a 7-min incubation with liver microsomes, most (96%) of the griseofulvin remained unchanged. Only small amounts of 4-desmethylgriseofulvin (1.26%) of dose) and 6-desmethylgriseofulvin (1.05% of dose) were formed. In isolated perfused liver, most of the drug (59% of dose) was excreted into bile within 4 hr, primarily as 4-desmethylgriseofulvin (24% of dose) and 6-methylgriseofulvin (24% of dose). In animals with bile duct cannulas, 65% of the dose was excreted into bile and 18% of the dose into urine within 4 hours. In bile, 32% of the dose was excreted as 4-desmethylgriseofulvin and 20% of the dose as 6-desmethylgriseofulvin, whereas in urine the drug was excreated predominantly as 6-desmethylgriseofulvin (13% of dose) with only a small amount of 4-desmethylgriseofulvin (1% of dose), during the first 4 hr. These results show that there is good correlation in the metabolic fate of 14C-griseofulvin in the liver microsomes, isolated perfused liver, and rats with bile duct cannulas. In addition to the similar ratio of 4-desmethylgriseofulvin to 6-desmethylgriseofulvin, there is also an agreement in the extent of metabolism and biliary excretion in isolated perfused liver and in rats with bile duct cannulas, which suggests that the isolated perfused liver is an important technique for studying drug metabolism in animals.

Animals↗
PubMed1975

Bile acids. XLVII. 12alpha-Hydroxylation of precursors of allo bile acids by rabbit liver microsomes.

Rabbit liver microsomal preparations fortified with 0.1 mM NADPH effectively promote hydroxylation of [3beta-3H]- or [24-14C]allochenodeoxycholic acid or [5alpha,6alpha-3H2]5alpha-cholestane-3alpha,7alpha-diol to their respective 12alpha-hydroxyl derivatives in yields of about 25 or 65% in 60 min. Minor amounts of other products are formed from the diol. The requirements for activity of rabbit liver microsomal 12alpha-hydroxylase resemble those of rat liver microsomes. Of a number of enzyme inhibitors studied only p-chloromercuribenzoate demonstrated a marked ability to inhibit the reaction with either tritiated substrate. There was no difference in the quantity of product produced from the tritiated acid or the 14C-labeled acid. No clear sex difference was found in activity of the enzyme, nor was an appreciable difference noted in activity of the enzyme between mature and immature animals.

Aging↗
PubMed1975

Dietary and hormonal effects upon activity of "soluble" protein and particulate fraction of fatty acid desaturation system of rat liver microsomes.

Rat liver microsomes were extracted with a buffered 0.15 M KCl and 0.25 M sucrose solution and fractionated by centrifugation into a particulate component and a supernatant containing a protein factor necessary for fatty acid desaturation. The delta 6 fatty acid desaturation activity of the extracted microsomes was reduced significantly, and the readdition of the supernatant restored the enzymatic activity to the original value of the whole microsomes. A protein diet or a fat-free diet increased the delta 6 desaturation activity of the whole microsomes. The activating effect was evoked upon the particulate components of the enzymatic desaturation system and not upon the protein factor present in the supernatant. Fasting, refeeding, and refeeding plus glucagon and theophylline treatments of rats also modified the delta 6 desaturation activity of whole liver microsomes. The effect also was evoked on the delta 6 desaturation system tightly bound to the microsomal membrane but not on the protein factor of the supernatant. Accordingly, the protein factor of the supernatant is considered to be different from the cyanide sensitive factor and the desaturase.

Animals↗
PubMed1979

Comparative study of the inductive effect of two psychomoderators--tetrabamate and complexe 1656--and of phenobarbital on liver microsomal enzymes in rats.

Tetrabamate (Atrium) and Complexe 1656, two psychosedative drugs, are complexes formed by phenobarbital with its N-substituted derivatives. We have studied the induction effect of all these compounds on the microsomal liver enzymes in male rats. Tetrabamate and Complexe 1656 were found to be equally effective in increasing the amount of microsomal proteins, cytochrome P-450 and the in vitro aniline p-hydroxylation and amino-pyrine N-demethylation activity. These effects were similar to those obtained after a treatment with an equivalent dose of phenobarbital. Febarbamate and difebarbamate had no significanteffect on microsomal enzymes. The inductive effect of tetrabamate and of its analogue seems essentially due to the phenobarbital content of these complexes.

Animals↗
PubMed1975

Localization of nascent NADPH-cytochrome c reductase in rat liver microsomes.

Rat liver microsomes incubated with [3H] puromycin in high salt buffer were digested with a mixture of protease, trypsin and chymotrypsin, in both the presence and absence of 1 % deoxycholate. Our observations revealed that the proteolysis of peptidyl puromycin labeled with [3H] puromycin was at least partially protected by the presence of microsomal membrane. Immuno-chemical analyses have further shown that most of the nascent NADPH-cytochrome c reductase in the microsomes was digested with the proteases while serum albumin was effectively protected from the digestion. It is thus proposed that NADPH-cytochrome c reductase synthesized on the membrane bound ribosomes is not transported to the vesicular cavity but directly to the outer surface of the microsomal membrane in a form which is accessible to the proteases.

Acyltransferases↗
PubMed1976

Phosphatidic acid metabolism in rat liver microsomes.

Rat liver microsomes contain phosphatidate phosphatases which split phosphatidic acid into inorganic phosphate and diacylglycerol and a system of phospholipases and lipases, which split phosphatidic acid into free fatty acids, glycerol and inorganic phosphate. In the presence of ATP,CoA and [1-14C]palmitate, part of the monoacyl-sn-glycerol 3-phosphate formed by phospholipase action is reesterified, yielding radioactive phosphatidic acid. The sum of di- and triacylglycerols formed from phosphatidic acid in the presence of ATP and CoA exceeded the amount of diacylglycerol formed in their absence. The yield of neutral lipids from sn-glycerol 3-phosphate and monoacyl-sn-glycerol 3-phosphate markedly exceeded that from phosphatidic acid. Comparison of the yields of di- and triacylglcerols from glycerol-labelled and fatty-acid-labelled phosphatidic acid was used to establish the extent of deacylation and reacylation. About 60% of the diacylglycerol was formed by direct dephosphorylation. The triacylglycerols, on the other hand, were formed almost exclusively from recycled phosphatidic acid.

Adenosine Triphosphate↗
PubMedDate not supplied

N-Hydroxylation of phenacetin by hamster liver microsomes.

Hamster liver microsomes have been shown to catalyze the N-hydroxylation of phenacetin. The reaction, which requires oxygen and NADPH, is inhibited by a carbon monoxide/oxygen atmosphere, indicating that it is catalyzed by a cytochrome P-450-dependent mixed-function oxidase. The N-hydroxyphenacetin can be further metabolized by the microsomes, and the reaction is inhibited by phenacetin.

Animals↗
PubMed1976

The effect of high sugar intake on the esterification of dihydroxyacetone phosphate by rat liver microsomes.

Rat liver microsomes were used as an enzyme source to study dietary-induced changes in the rate of dihydroxyacetone phosphate esterification. Rats were fed (1) 75% glucose or fructose diets for various time intervals, or (2) fed a fractose diet for six days and then a chow diet. Both the glucose and fructose diets produced a 2--3-fold increase in total and neutral glycerolipid formation from dihydroxyacetone phosphate measured in the presence of ATP, palmitate, CoA, and NADH. The increased rate of dihydroxyacetone phosphate esterification and a simultaneous rise in serum triglyceride level in rats fed fructose was rapidly reversed when chow was substituted for the fructose. The results indicate that an increased rate of dihyroxyacetone phosphate esterification may contribute to the acceleration of endogenous glycerolipid biosynthesis noted under these dietary conditions.

Animals↗
PubMed1976

Transfer of xylose to steroids by rabbit liver microsomes.

Rabbit liver microsomal preparations can transfer xylose from UDP-xylose to estron, 17alpha-estradiol, and 17beta-estradiol, and, in poorer yield, to diethylstilbestrol and p-nitrophenol. No transfer of xylose to estriol, testosterone, epitestosterone or 17alpha-estradiol 3-glucuronide could be demonstrated. The xyloside of [6,7-3H]estrone which was formed by liver microsomes crystallized to constant specific activity with estrone beta-D-xylopyranoside, the chemical preparation of which is described.

Animals↗
PubMed1992

Immunochemical characterization of a cytochrome P450 isozyme and a protein purified from liver microsomes of male guinea pigs and their roles in the oxidative metabolism of delta 9-tetrahydrocannabinol by guinea pig liver microsomes.

A protein (designated as protein-B) was purified from liver microsomes of adult male guinea pigs by an affinity chromatography with omega-aminooctyl Sepharose 4B, followed by HPLC using DEAE-5PW and hydroxyapatite columns which had been used to purify a cytochrome P450 (P450) isozyme (P450-A) from the same subcellular fraction (Narimatsu et al., Biochem Biophys Res Commun 172: 607-613, 1990). Protein-B had a molecular mass of 49 kDa in SDS-PAGE, but did not show absorbance at 417 nm for heme. Further, it did not show any oxidative activities towards aniline (AN), d-benzphetamine (d-BP), p-nitroanisole (p-NA) or delta 9-tetrahydrocannabinol (delta 9-THC) in a reconstituted system including dilauroylphosphatidylcholine, NADPH-P450 reductase, and cytochrome b5. However, antiserum against protein-B raised in rabbits suppressed liver microsomal oxidative activities towards d-BP and p-NA dose-dependently. The antibody decreased delta 9-THC oxidative activity most effectively, but did not decrease AN hydroxylation activity. Antiserum against P450-A suppressed all the activities towards these four substrates, especially towards delta 9-THC, in liver microsomes of male guinea pigs. Moreover, reconstitution with hemin made it possible for protein-B to produce some oxidative activity toward delta 9-THC. These results suggest that protein-B is also a cytochrome P450 isozyme which has lost a heme moiety during purification steps. Both P450-A and protein-B could have a role as cytochrome P450 isozymes in the oxidative metabolism of drugs, especially that of delta 9-THC by the liver microsomes of adult male guinea pigs.

Amino Acid Sequence↗